Process for producing silica-based film, silica-based film, insulating film, and semiconductor device

ABSTRACT

A process for producing a silica-based film which comprises irradiating a film comprising at least one siloxane compound with electron beams to thereby convert the film into a film having a dielectric constant of 3 or lower and having silicon carbide bonds represented by Si—C—Si is disclosed. The film has an even thickness, is excellent in storage stability, dielectric constant, mechanical strength, etc., has low hygroscopicity, and is suitable for use as a dielectric film in semiconductor devices and the like.

FIELD OF THE INVENTION

The present invention relates to a process for producing a film. Moreparticularly, the invention relates to a process capable of giving acoating film which is excellent in dielectric constant, mechanicalstrength, and low hygroscopicity, and is suitable for use as adielectric film in semiconductor devices and the like.

BACKGROUND OF THE INVENTION

Silica (SiO₂) films formed by vacuum processes such as the CVD methodhave hitherto been used frequently as dielectric films in semiconductordevices and other devices. In recent years, a dielectric film whichcomprises a tetraalkoxysilane hydrolyzate as the main component and iscalled an SOG (spin on glass) film has come to be used for the purposeof forming a more even dielectric film. Furthermore, as a result of thetrend toward higher degree of integration in semiconductor devices andthe like, a dielectric film called an organic SOG film has beendeveloped which comprises a polyorganosiloxane as the main component andhas a low dielectric constant.

However, with further progress in the high integration or multilayerfilm interconnection in semiconductor devices and the like, betterelectrical insulation between metal lines and vias has come to berequired and, hence, a dielectric film has come to be desired which hassatisfactory storage stability, a lower dielectric constant, andexcellent leakage current characteristics.

JP-A-6-181201 (the term “JP-A” as used herein means an “unexaminedpublished Japanese patent application”) discloses a dielectric filmhaving a lower dielectric constant. This technique is intended toprovide an insulating film for semiconductor devices which has low waterabsorption and excellent cracking resistance. This insulating film isformed from a composition which comprises as the main component anoligomer having a number average molecular weight of 500 or higherobtained by condensation-polymerizing an organometallic compoundcontaining at least one element selected from titanium, zirconium,niobium, and tantalum with an organosilicon compound having at least onealkoxyl group in the molecule.

JP-A-10-237307 and WO 97/00535 disclose techniques for curing an SOGfilm with electron beams, which comprise irradiating a resin comprisinga siloxane resin as the main component with electron beams. Thesetechniques are intended to convert a siloxane resin into silica (SiO₂)by electron beam irradiation. The insulating film thus obtained usuallyhas a dielectric constant of from 3.5 to 4.2, which is still too high toapply the insulating film to semiconductor devices which operate at ahigh frequency.

SUMMARY OF THE INVENTION

Accordingly, one object of the invention is to provide a process forfilm production for eliminating the problem described above. Moreparticularly, the object is to provide a process for producing aninsulating film which has an excellent balance between dielectricconstant and mechanical strength and is suitable for use as a dielectricfilm in semiconductor devices and the like.

Another object of the invention is to provide a process for producing asilica-based film which comprises irradiating a film comprising at leastone siloxane compound with electron beams.

Still another object of the invention is to provide a film obtained bythe process and an insulating film.

DETAILED DESCRIPTION OF THE INVENTION

In the invention, a film comprising at least one siloxane compound(hereinafter referred to as “coating film”) is formed on a substrate.

For forming the coating film, a coating composition prepared bydissolving at least one siloxane compound in an organic solvent(hereinafter referred to as “coating composition”) is applied to asubstrate and the organic solvent is removed from the coating.

Ingredient (A) which is the siloxane compound in the invention is aproduct of the hydrolysis and/or condensation of at least one compoundselected from the group consisting of compounds represented by thefollowing formula (1) (hereinafter referred to as “compounds (1)”):R¹ _(a)Si(OR²)_(4-a)  (1)wherein R¹ represents a hydrogen atom or a monovalent organic group; R²represents a monovalent organic group; and a Is an integer of 0 to 2,and compounds represented by the following formula (2) (hereinafterreferred to as “compounds (2)”):R³ _(b)(R⁴O)_(3-b)Si—(R⁷)_(d)—Si(OR⁵)_(3-c)R⁶ _(c)  (2)wherein R³, R⁴, R⁵, and R⁶ may be the same or different and eachrepresents a monovalent organic group; b and c may be the same ordifferent and each is an integer of 0 to 2; R⁷ represents an oxygen atomor a group represented by —(CH₂)_(n)—, wherein n is 1 to 6; and d is 0or 1.

Examples of the monovalent organic groups represented by R¹ and R² informula (1) include alkyl, aryl, allyl, and glycidyl groups. In formula(1), R¹ is preferably a monovalent organic group, more preferably analkyl or phenyl group.

The alkyl group preferably has 1 to 5 carbon atoms, and examples thereofinclude methyl, ethyl, propyl, and butyl. Those alkyl groups may belinear or branched, and may be ones in which one or more of the hydrogenatoms have been replaced, for example, with fluorine atoms.

In formula (1), examples of the aryl group include phenyl, naphthyl,methylphenyl, ethylphenyl, chlorophenyl, bromophenyl, and fluorophenyl.

Specific examples of the compounds represented by formula (1) include:

trialkoxysilanes such as trimethoxysilane, triethoxysilane,tri-n-propoxysilane, triisopropoxysilane, tri-n-butoxysilane,tri-sec-butoxysilane, tri-tert-butoxysilane, triphenoxysilane,fluorotrimethoxysilane, fluorotriethoxysilane,fluorotri-n-propoxysilane, fluorotriisopropoxysilane,fluorotri-n-butoxysilane, fluorotri-sec-butoxysilane,fluorotri-tert-butoxysilane, and fluorotriphenoxysilane;tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane,tetra-n-propoxysilane, tetraisopropoxysilane tetra-n-butoxysilane,tetra-sec-butoxysilane, tetra-tert-butoxysilane, and tetraphenoxysilane;alkyltrialkoxysilanes such as methyltrimethoxysilane,methyltriethoxysilane, methyltri-n-propoxysilane,methyltriisopropoxysilane, methyltri-n-butoxysilane,methyltri-sec-butoxysilane, methyltri-tert-butoxysilane,methyltriphenoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane,ethyltri-n-propoxysilane, ethyltriisopropoxysilane,ethyltri-n-butoxysilane, ethyltri-sec-butoxysilane,ethyltri-tert-butoxysilane, ethyltriphenoxysilane,vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri-n-propoxysilane,vinyltriisopropoxysilane, vinyltri-n-butoxysilane,vinyltri-sec-butoxysilane, vinyltri-tert-butoxysilane,vinyltriphenoxysilane, n-propyltrimethoxysilane,n-propyltriethoxysilane, n-propyltri-n-propoxysilane,n-propyltriisopropoxysilane, n-propyltri-n-butoxysilane,n-propyltri-sec-butoxysilane, n-propyltri-tert-butoxysilane,n-propyltriphenoxysilane, isopropyltrimethoxysilane,isopropyltriethoxysilane, isopropyltri-n-propoxysilane,isopropyltriisopropoxysilane, isopropyltri-n-butoxysilane,isopropyltri-sec-butoxysilane, isopropyltri-tert-butoxysilane,isopropyltriphenoxysilane, n-butyltrimethoxysilane,n-butyltriethoxysilane, n-butyltri-n-propoxysilane,n-butyltriisopropoxysilane, n-butyltri-n-butoxysilane,n-butyltri-sec-butoxysilane, n-butyltri-tert-butoxysilane,n-butyltriphenoxysilane, sec-butyltrimethoxysilane,sec-butyltriethoxysilane, sec-butyltri-n-propoxysilane,sec-butyltriisopropoxysilane, sec-butyltri-n-butoxysilane,sec-butyltri-sec-butoxysilane, sec-butyltri-tert-butoxysilane,sec-butyltriphenoxysilane, tert-butyltrimethoxysilane,tert-butyltriethoxysilane, tert-butyltri-n-propoxysilane,tert-butyltriisopropoxysilane, tert-butyltri-n-butoxysilane,tert-butyltri-sec-butoxysilane, and tert-butyltri-tert-butoxysilane;tert-butyltriphenoxysilane, phenyltrimethoxysilane,phenyltriethoxysilane, phenyltri-n-propoxysilane,phenyltriisopropoxysilane, phenyltri-n-butoxysilane,phenyltri-sec-butoxysilane, phenyltri-tert-butoxysilane,phenyltriphenoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane,γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane,γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane,γ-trifluoropropyltrimethoxysilane, and γ-trifluoropropyltriethoxysilane;and dimethyldimethoxysilane, dimethyldiethoxysilane,dimethyldi-n-propoxysilane, dimethyldiisopropoxysilane,dimethyldi-n-butoxysilane, dimethyldi-sec-butoxysilane,dimethyldi-tert-butoxysilane, dimethyldiphenoxysilane,diethyldimethoxysilane, diethyldiethoxysilane,diethyldi-n-propoxysilane, diethyldiisopropoxysilane,diethyldi-n-butoxysilane, diethyldi-sec-butoxysilane,diethyldi-tert-butoxysilane, diethyldiphenoxysilane,di-n-propyldimethoxysilane, di-n-propyldiethoxysilane,di-n-propyldi-n-propoxysilane, di-n-propyldiisopropoxysilane,di-n-propyldi-n-butoxysilane, di-n-propyldi-sec-butoxysilane,di-n-propyldi-tert-butoxysilane, di-n-propyldiphenoxysilane,diisopropyldimethoxysilane, diisopropyldiethoxysilane,diisopropyldi-n-propoxysilane, diisopropyldiisopropoxysilane,diisopropyldi-n-butoxysilane, diisopropyldi-sec-butoxysilane,diisopropyldi-tert-butoxysilane, diisopropyldiphenoxysilane,di-n-butyldimethoxysilane, di-n-butyldiethoxysilane,di-n-butyldi-n-propoxysilane, di-n-butyldiisopropoxysilane,di-n-butyldi-n-butoxysilane, di-n-butyldi-sec-butoxysilane,di-n-butyldi-tert-butoxysilane, di-n-butyldiphenoxysilane,di-sec-butyldimethoxysilane, di-sec-butyldiethoxysilane,di-sec-butyldi-n-propoxysilane, di-sec-butyldiisopropoxysilane,di-sec-butyldi-n-butoxysilane, di-sec-butyldi-sec-butoxysilane,di-sec-butyldi-tert-butoxysilane, di-sec-butyldiphenoxysilane,di-tert-butyldimethoxysilane, di-tert-butyldiethoxysilane,di-tert-butyldi-n-propoxysilane, di-tert-butyldiisopropoxysilane,di-tert-butyldi-n-butoxysilane, di-tert-butyldi-sec-butoxysilane,di-tert-butyldi-tert-butoxysilane, di-tert-butyldiphenoxysilane,diphenyldimethoxysilane, diphenyldiethoxysilane,diphenyldi-n-propoxysilane, diphenyldiisopropoxysilane,diphenyldi-n-butoxysilane, diphenyldi-sec-butoxysilane,diphenyldi-tert-butoxysilane, diphenyldiphenoxysilane,divinyltrimethoxysilane, γ-aminopropyltrimethoxysilane,γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane,γ-glycidoxypropyltriethoxysilane, γ-trifluoropropyltrimethoxysilane, andγ-trifluoropropyltriethoxysilane.

Preferred of those compounds (1) are tetramethoxysilane,tetraethoxysilane, tetra-n-propoxysilane, tetraisopropoxysilane,tetraphenoxysilane, methyltrimethoxysilane, methyltriethoxysilane,methyltri-n-propoxysilane, methyltriisopropoxysilane,ethyltrimethoxysilane, ethyltriethoxysilane, vinyltrimethoxysilane,vinyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane,dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldimethoxysilane,diethyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane,trimethylmonomethoxysilane, trimethylmonoethoxysilane,triethylmonomethoxysilane, triethylmonoethoxysilane,triphenylmonomethoxysilane, and triphenylmonoethoxysilane.

In formula (2), examples of the monovalent organic group include thesame organic groups as those enumerated above with regard to formula(1).

Examples of the divalent organic group represented by R⁷ in formula (2)include alkylene groups having 2 to 6 carbon atoms, such as methylene.

Examples of the compounds represented by formula (2) wherein R⁷ is anoxygen atom include hexamethoxydisiloxane, hexaethoxydisiloxane,hexaphenoxydisiloxane, 1,1,1,3,3-pentamethoxy-3-methyldisiloxane,1,1,1,3,3-pentaethoxy-3-methyldisiloxane,1,1,1,3,3-pentamethoxy-3-phenyldisiloxane,1,1,1,3,3-pentaethoxy-3-phenyldisiloxane,1,1,3,3-tetramethoxy-1,3-dimethyldisiloxane,1,1,3,3-tetraethoxy-1,3-dimethyldisiloxane,1,1,3,3-tetramethoxy-1,3-diphenyldisiloxane,1,1,3,3-tetraethoxy-1,3-diphenyldisiloxane,1,1,3-trimethoxy-1,3,3-trimethyldisiloxane,1,1,3-triethoxy-1,3,3-trimethyldisiloxane,1,1,3-trimethoxy-1,3,3-triphenyldisiloxane,1,1,3-triethoxy-1,3,3-triphenyldisiloxane,1,3-dimethoxy-1,1,3,3-tetramethyldisiloxane,1,3-diethoxy-1,1,3,3-tetramethyldisiloxane,1,3-dimethoxy-1,1,3,3-tetraphenyldisiloxane, and1,3-diethoxy-1,1,3,3-tetraphenyldisiloxane. Preferred of these arehexamethoxydisiloxane, hexaethoxydisiloxane,1,1,3,3-tetramethoxy-1,3-dimethyldisiloxane,1,1,3,3-tetraethoxy-1,3-dimethyldisiloxane,1,1,3,3-tetramethoxy-1,3-diphenyldisiloxane,1,3-dimethoxy-1,1,3,3-tetramethyldisiloxane,1,3-diethoxy-1,1,3,3-tetramethyldisiloxane,1,3-dimethoxy-1,1,3,3-tetraphenyldisiloxane,1,3-diethoxy-1,1,3,3-tetraphenyldisiloxane, and the like.

Examples of the compounds represented by formula (2) wherein d is 0include hexamethoxydisilane, hexaethoxydisilane, hexaphenoxydisilane,1,1,1,2,2-pentamethoxy-2-methyldisilane,1,1,1,2,2-pentaethoxy-2-methyldisilane,1,1,1,2,2-pentamethoxy-2-phenyldisilane,1,1,1,2,2-pentaethoxy-2-phenyldisilane,1,1,2,2-tetramethoxy-1,2-dimethyldisilane,1,1,2,2-tetraethoxy-1,2-dimethyldisilane,1,1,2,2-tetramethoxy-1,2-diphenyldisilane,1,1,2,2-tetraethoxy-1,2-diphenyldisilane,1,1,2-trimethoxy-1,2,2-trimethyldisilane,1,1,2-triethoxy-1,2,2-trimethyldisilane,1,1,2-trimethoxy-1,2,2-triphenyldisilane,1,1,2-triethoxy-1,2,2-triphenyldisilane,1,2-dimethoxy-1,1,2,2-tetramethyldisilane,1,2-diethoxy-1,1,2,2-tetramethyldisilane,1,2-dimethoxy-1,1,2,2-tetraphenyldisilane, and1,2-diethoxy-1,1,2,2-tetraphenyldisilane.

Examples of the compounds represented by formula (2) wherein R⁷ is agroup represented by —(CH₂)_(n)— include bis(hexamethoxysilyl)methane,bis(hexaethoxysilyl)methane, bis(hexaphenoxysilyl)methane,bis(dimethoxymethylsilyl)methane, bis(diethoxymethylsilyl)methane,bis(dimethoxyphenylsilyl)methane, bis(diethoxyphenylsilyl)methane,bis(methoxydimethylsilyl)methane, bis(ethoxydimethylsilyl)methane,bis(methoxydiphenylsilyl)methane, bis(ethoxydiphenylsilyl)methane,bis(hexamethoxysilyl)ethane, bis(hexaethoxysilyl)ethane,bis(hexaphenoxysilyl)ethane, bis(dimethoxymethylsilyl)ethane,bis(diethoxymethylsilyl)ethane, bis(dimethoxyphenylsilyl)ethane,bis(diethoxyphenylsilyl)ethane, bis(methoxydimethylsilyl)ethane,bis(ethoxydimethylsilyl)ethane, bis(methoxydiphenylsilyl)ethane,bis(ethoxydiphenylsilyl)ethane, 1,3-bis(hexamethoxysilyl)propane,1,3-bis(hexaethoxysilyl)propane, 1,3-bis(hexaphenoxysilyl)propane,1,3-bis(dimethoxymethylsilyl)propane,1,3-bis(diethoxymethylsilyl)propane,1,3-bis(dimethoxyphenylsilyl)propane,1,3-bis(diethoxyphenylsilyl)propane,1,3-bis(methoxydimehylsilyl)propane,1,3-bis(ethoxydimethylsilyl)propane,1,3-bis(methoxydiphenylsilyl)propane, and1,3-bis(ethoxydiphenylsilyl)propane. Preferred of these arehexamethoxydisilane, hexaethoxydisilane, hexaphenoxydisilane,1,1,2,2-tetramethoxy-1,2-dimethyldisilane,1,1,2,2-tetraethoxy-1,2-dimethyldisilane,1,1,2,2-tetramethoxy-1,2-diphenyldisilane,1,1,2,2-tetraethoxy-1,2-diphenyldisilane,1,2-dimethoxy-1,1,2,2-tetramethyldisilane,1,2-diethoxy-1,1,2,2-tetramethyldisilane,1,2-dimethoxy-1,1,2,2-tetraphenyldisilane,1,2-diethoxy-1,1,2,2-tetraphenyldisilane, bis(hexamethoxysilyl)methane,bis(hexaethoxysilyl)methane, bis(dimethoxymethylsilyl)methane,bis(diethoxymethylsilyl)methane, bis(dimethoxyphenylsilyl)methane,bis(diethoxyphenylsilyl)methane, bis(methoxydimethylsilyl)methane,bis(ethoxydimethylsilyl)methane, bis(methoxydiphenylsilyl)methane, andbis(ethoxydiphenylsilyl)methane.

In the invention, it is preferred to use a combination of analkyltrialkoxysilane and a tetraalkoxysilane among the compounds (1) and(2) enumerated above. In this case, the proportion of thetetraalkoxysilane is generally from 5 to 75% by weight, preferably from10 to 70% by weight, more preferably from 15 to 70% by weight, and thatof the alkyltrialkoxysilane is generally from 25 to 95% by weight,preferably from 30 to 90% by weight, more preferably from 30 to 85% byweight, in terms of the amount of the product of complete hydrolysis andcondensation. When a tetraalkoxysilane and a trialkoxysilane are used ina proportion within that range, the coating film obtained has a highmodulus of elasticity and an exceedingly low dielectric constant.

The term “product of complete hydrolysis and condensation” as usedherein means a product in which all the R²O—, R⁴O—, and R⁵O— groups inthe compounds (1) and (2) have been hydrolyzed into SiOH groups andcompletely condensed to form a siloxane structure.

The compounds (1) and (2) are hydrolyzed and condensed in an organicsolvent. Water is preferably used in the hydrolysis and condensation inan amount of from 0.3 to 10 mol per mol of the groups represented byR²O—, R⁴O—, and R⁵O— in formulae (1) and (2).

A catalyst is generally used for the hydrolysis and condensation of thecompounds (1) and (2) in an organic solvent.

Examples of the catalyst include organic acids, inorganic acids, organicbases, inorganic bases, and metal chelates.

Examples of the organic acids include acetic acid, propionic acid,butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoicacid, nonanoic acid, decanoic acid, oxalic acid, maleic acid,methylmalonic acid, adipic acid, sebacic acid, gallic acid, butyricacid, mellitic acid, arachidonic acid, shikimic acid, 2-ethylhexanoicacid, oleic acid, stearic acid, linoleic acid, linolenic acid, salicylicacid, benzoic acid, p-aminobenzoic acid, p-toluenesulfonic acid,benzenesulfonic acid, monochloroacetic acid, dichloroacetic acid,trichloroacetic acid, trifluoroacetic acid, formic acid, malonic acid,sulfonic acids, phthalic acid, fumaric acid, citric acid, and tartaricacid.

Examples of the inorganic acids include hydrochloric acid, nitric acid,sulfuric acid, hydrofluoric acid, and phosphoric acid.

Examples of the inorganic bases include ammonia, sodium hydroxide,potassium hydroxide, barium hydroxide, and calcium hydroxide.

Examples of the organic bases include methanolamine, ethanolamine,propanolamine, butanolamine, N-methylmethanolamine,N-ethylmethanolamine, N-propylmethanolamine, N-butylmethanolamine,N-methylethanolamine, N-ethylethanolamine, N-propylethanolamine,N-butylethanolamine, N-methylpropanolamine, N-ethylpropanolamine,N-propylpropanolamine, N-butylpropanolamine, N-methylbutanolamine,N-ethylbutanolamine, N-propylbutanolamine, N-butylbutanolamine,N,N-dimethylmethanolamine, N,N-diethylmethanolamine,N,N-dipropylmethanolamine, N,N-dibutylmethanolamine,N,N-dimethylethanolamine, N,N-diethylethanolamine,N,N-dipropylethanolamine, N,N-dibutylethanolamine,N,N-dimethylpropanolamine, N,N-diethylpropanolamine,N,N-dipropylpropanolamine, N,N-dibutylpropanolamine,N,N-dimethylbutanolamine, N,N-diethylbutanolamine,N,N-dipropylbutanolamine, N,N-dibutylbutanolamine,N-methyldimethanolamine, N-ethyldimethanolamine,N-propyldimethanolamine, N-butyldimethanolamine, N-methyldiethanolamine,N-ethyldiethanolamine, N-propyldiethanolamine, N-butyldiethanolamine,N-methyldipropanolamine, N-ethyldipropanolamine,N-propyldipropanolamine, N-butyldipropanolamine, N-methyldibutanolamine,N-ethyldibutanolamine, N-propyldibutanolamine, N-butyldibutanolamine,N-(aminomethyl)methanolamine, N-(aminomethyl)ethanolamine,N-(aminomethyl)propanolamine, N-(aminomethyl)butanolamine,N-(aminoethyl)methanolamine, N-(aminoethyl)ethanolamine,N-(aminoethyl)propanolamine, N-(aminoethyl)butanolamine,N-(aminopropyl)methanolamine, N-(aminopropyl)ethanolamine,N-(aminopropyl)propanolamine, N-(aminopropyl)butanolamine,N-(aminobutyl)methanolamine, N-(aminobutyl)ethanolamine,N-(aminobutyl)propanolamine, N-(aminobutyl)butanolamine,methoxymethylamine, methoxyethylamine, methoxypropylamine,methoxybutylamine, ethoxymethylamine, ethoxyethylamine,ethoxypropylamine, ethoxybutylamine, propoxymethylamine,propoxyethylamine, propoxypropylamine, propoxybutylamine,butoxymethylamine, butoxyethylamine, butoxypropylamine,butoxybutylamine, methylamine, ethylamine, propylamine, butylamine,N,N-dimethylamine, N,N-diethylamine, N,N-dipropylamine,N,N-dibutylamine, trimethylamine, triethylamine, tripropylamine,tributylamine, tetramethylammonium hydroxide, tetraethylammoniumhydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide,tetramethylethylenediamine, tetraethylethylenediamine,tetrapropylethylenediamine, tetrabutylethylenediamine,methylaminomethylamine, methylaminoethylamine, methylaminopropylamine,methylaminobutylamine, ethylaminomethylamine, ethylaminoethylamine,ethylaminopropylamine, ethylaminobutylamine, propylaminomethylamine,propylaminoethylamine, propylaminopropylamine, propylaminobutylamine,butylaminomethylamine, butylaminoethylamine, butylaminopropylamine,butylaminobutylamine, pyridine, pyrrole, piperazine, pyrrolidine,piperidine, picoline, morpholine, methylmorpholine, diazabicyclooctane,diazabicyclononane, diazabicycloundecene, and urea.

Examples of the metal chelates include titanium chelate compounds suchas triethoxymono(acetylacetonato)titanium,tri-n-propoxymono(acetylacetonato)titanium,triisopropoxymono(acetylacetonato)titanium,tri-n-butoxymono(acetylacetonato)titanium,tri-sec-butoxymono(acetylacetonato)titanium,tri-tert-butoxymono(acetylacetonato)titanium,diethoxybis(acetylacetonato)titanium,di-n-propoxybis(acetylacetonato)titanium,diisopropoxybis(acetylacetonato)titanium,di-n-butoxybis(acetylacetonato)titanium,di-sec-butoxybis(acetylacetonato)titanium,di-tert-butoxybis(acetylacetonato)titanium,monoethoxytris(acetylacetonato)titanium,mono-n-propoxytris(acetylacetonato)titanium,monoisopropoxytris(acetylacetonato)titanium,mono-n-butoxytris(acetylacetonato)titanium,mono-sec-butoxytris(acetylacetonato)titanium,mono-tert-butoxytris(acetylacetonato)titanium,tetrakis(acetylacetonato)titanium,triethoxymono(ethylacetoacetato)titanium,tri-n-propoxymono(ethylacetoacetato)titanium,triisopropoxymono(ethylacetoacetato)titanium,tri-n-butoxymono(ethylacetoacetato)titanium,tri-sec-butoxymono(ethylacetoacetato)titanium,tri-tert-butoxymono(ethylacetoacetato)titanium,diethoxybis(ethylacetoacetato)titanium,di-n-propoxybis(ethylacetoacetato)titanium,diisopropoxybis(ethylacetoacetato)titanium,di-n-butoxybis(ethylacetoacetato)titanium,di-sec-butoxybis(ethylacetoacetato)titanium,di-tert-butoxybis(ethylacetoacetato)titanium,monoethoxytris(ethylacetoacetato)titanium,mono-n-propoxytris(ethylacetoacetato)titanium,monoisopropoxytris(ethylacetoacetato)titanium,mono-n-butoxytris(ethylacetoacetato)titanium,mono-sec-butoxytris(ethylacetoacetato)titanium,mono-tert-butoxytris(ethylacetoacetato)titanium,tetrakis(ethylacetoacetato)titanium,mono(acetylacetonato)tris(ethylacetoacetato)titanium,bis(acetylacetonato)bis(ethylacetoacetato)titanium, andtris(acetylacetonato)mono(ethylacetoacetato)titanium; zirconium chelatecompounds such as triethoxymono(acetylacetonato)zirconium,tri-n-propoxymono(acetylacetonato)zirconium,triisopropoxymono(acetylacetonato)zirconium,tri-n-butoxymono(acetylacetonato)zirconium,tri-sec-butoxymono(acetylacetonato)zirconium,tri-tert-butoxymono(acetylacetonato)zirconium,diethoxybis(acetylacetonato)zirconium,di-n-propoxybis(acetylacetonato)zirconium,diisopropoxybis(acetylacetonato)zirconium,di-n-butoxybis(acetylacetonato)zirconium,di-sec-butoxybis(acetylacetonato)zirconium,di-tert-butoxybis(acetylacetonato)zirconium,monoethoxytris(acetylacetonato)zirconium,mono-n-propoxytris(acetylacetonato)zirconium,monoisopropoxytris(acetylacetonato)zirconium,mono-n-butoxytris(acetylacetonato)zirconium,mono-sec-butoxytris(acetylacetonato)zirconium,mono-tert-butoxytris(acetylacetonato)zirconium,tetrakis(acetylacetonato)zirconium,triethoxymono(ethylacetoacetato)zirconium,tri-n-propoxymono(ethylacetoacetato)zirconium,triisopropoxymono(ethylacetoacetato)zirconium,tri-n-butoxymono(ethylacetoacetato)zirconium,tri-sec-butoxymono(ethylacetoacetato)zirconium,tri-tert-butoxymono(ethylacetoacetato)zirconium,diethoxybis(ethylacetoacetato)zirconium,di-n-propoxybis(ethylacetoacetato)zirconium,diisopropoxybis(ethylacetoacetato)zirconium,di-n-butoxybis(ethylacetoacetato)zirconium,di-sec-butoxybis(ethylacetoacetato)zirconium,di-tert-butoxybis(ethylacetoacetato)zirconium,monoethoxytris(ethylacetoacetato)zirconium,mono-n-propoxytris(ethylacetoacetato)zirconium,monoisopropoxytris(ethylacetoacetato)zirconium,mono-n-butoxytris(ethylacetoacetato)zirconium,mono-sec-butoxytris(ethylacetoacetato)zirconium,mono-tert-butoxytris(ethylacetoacetato)zirconium,tetrakis(ethylacetoacetato)zirconium,mono(acetylacetonato)tris(ethylacetoacetato)zirconium,bis(acetylacetonato)bis(ethylacetoacetato)zirconium, andtris(acetylacetonato)mono(ethylacetoacetato)zirconium; and aluminumchelate compounds such as tris(acetylacetonato)aluminum andtris(ethylacetoacetato)aluminum.

The amount of the catalyst to be used is generally from 0.0001 to 1 mol,preferably from 0.001 to 0.1 mol, per mol of the total amount of thecompounds (1) and (2).

In the case where the siloxane compound is a condensate, it preferablyhas a weight-average molecular weight, calculated for standardpolystyrene, of from 500 to 100,000.

In the invention, the siloxane compound is usually dissolved in anorganic solvent and applied as a coating composition.

Examples of the solvent which can be used in the invention includealiphatic hydrocarbon solvents such as n-pentane, isopentane, n-hexane,isohexane, n-heptane, isoheptane, 2,2,4-trimethylpentane, n-octane,isooctane, cyclohexane, and methylcyclohexane; aromatic hydrocarbonsolvents such as benzene, toluene, xylene, ethylbenzene,trimethylbenzene, methylethylbenzene, n-propylbenzene, isopropylbenzene,diethylbenzene, isobutylbenzene, triethylbenzene, diisopropylbenzene,n-amylnaphthalene, and trimethylbenzene; monohydric alcohols such asmethanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol,sec-butanol, t-butanol, n-pentanol, isopentanol, 2-methylbutanol,sec-pentanol, t-pentanol, 3-methoxybutanol, n-hexanol, 2-methylpentanol,sec-hexanol, 2-ethylbutanol, sec-heptanol, heptanol-3, n-octanol,2-ethylhexanol, sec-octanol, n-nonyl alcohol, 2,6-dimethylheptanol-4,n-decanol, sec-undecyl alcohol, trimethylnonyl alcohol, sec-tetradecylalcohol, sec-heptadecyl alcohol, phenol, cyclohexanol,methylcyclohexanol, 3,3,5-trimethylcyclohexanol, benzyl alcohol,phenylmethylcarbinol diacetone alcohol, and cresol; polyhydric alcoholssuch as ethylene glycol, 1,2-propylene glycol, 1,3-butylene glycol,pentanediol-2,4, 2-methylpentanediol-2,4, hexanediol-2,5,heptanediol-2,4, 2-ethylhexanediol-1,3, diethylene glycol, dipropyleneglycol, triethylene glycol, tripropylene glycol, and glycerol; ketonesolvents such as acetone, methyl ethyl ketone, methyl n-propyl ketone,methyl n-butyl ketone, diethyl ketone, methyl isobutyl ketone, methyln-pentyl ketone, ethyl n-butyl ketone, methyl n-hexyl ketone, diisobutylketone, trimethylnonanone, cyclohexanone, methylcyclohexanone,2,4-pentanedione, acetonylacetone, diacetone alcohol, acetophenone, andfenchone; ether solvents such as ethyl ether, isopropyl ether, n-butylether, n-hexyl ether, 2-ethylhexyl ether, ethylene oxide, 1,2-propyleneoxide, dioxolane, 4-methyldioxolane, dioxane, dimethyldioxane, ethyleneglycol monomethyl ether, ethylene glycol monoethyl ether, ethyleneglycol diethyl ether, ethylene glycol mono-n-butyl ether, ethyleneglycol mono-n-hexyl ether, ethylene glycol monophenyl ether, ethyleneglycol mono-2-ethylbutyl ether, ethylene glycol dibutyl ether,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol diethyl ether, diethylene glycol mono-n-butyl ether,diethylene glycol di-n-butyl ether, diethylene glycol mono-n-hexylether, ethoxytriglycol, tetraethylene glycol di-n-butyl ether, propyleneglycol monomethyl ether, propylene glycol monoethyl ether, propyleneglycol monopropyl ether, propylene glycol monobutyl ether, dipropyleneglycol monomethyl ether, dipropylene glycol monoethyl ether,tripropylene glycol monomethyl ether, tetrahydrofuran, and2-methyltetrahydrofuran; ester solvents such as diethyl carbonate,methyl acetate, ethyl acetate, γ-butyrolactone, γ-valerolactone,n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate,sec-butyl acetate, n-pentyl acetate, sec-pentyl acetate, 3-methoxybutylacetate, methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexylacetate, benzyl acetate, cyclohexyl acetate, methylcyclohexyl acetate,n-nonyl acetate, methyl acetoacetate, ethyl acetoacetate, ethyleneglycol monomethyl ether acetate, ethylene glycol monoethyl etheracetate, diethylene glycol monomethyl ether acetate, diethylene glycolmonoethyl ether acetate, diethylene glycol mono-n-butyl ether acetate,propylene glycol monomethyl ether acetate, propylene glycol monoethylether acetate, propylene glycol monopropyl ether acetate, propyleneglycol monobutyl ether acetate, dipropyl glycol monomethyl etheracetate, dipropylene glycol monoethyl ether acetate, glycol diacetate,methoxytriglycol acetate, ethyl propionate, n-butyl propionate, isoamylpropionate, diethyl oxalate, di-n-butyl oxalate, methyl lactate, ethyllactate, n-butyl lactate, n-amyl lactate, diethyl malonate, dimethylphthalate, and diethyl phthalate; nitrogen-containing solvents such asN-methylformamide, N,N-dimethylformamide, N,N-diethylformamide,acetamide, N-methylacetamide, N,N-dimethylacetamide,N-methylpropionamide, and N-methylpyrrolidone; and sulfur-containingsolvents such as dimethyl sulfide, diethyl sulfide, thiophene,tetrahydrothiophene, dimethyl sulfoxide, sulfolane, and1,3-propanesultone. These solvents can be used alone or as a mixture oftwo or more thereof.

It is especially preferred in the invention to use an organic solventhaving a boiling point lower than 250° C. Examples thereof includealcohols such as methanol, ethanol, and isopropanol; polyhydric alcoholssuch as ethylene glycol and glycerol; glycol ether solvents such asethylene glycol monomethyl ether, ethylene glycol monobutyl ether,diethyl glycol monoethyl ether, diethylene glycol diethyl ether,propylene glycol monopropoyl ether, and dipropylene glycol monoethylether; glycol acetate/ether solvents such as ethylene glycol monomethylether acetate, diethylene glycol monobutyl ether acetate, ethyleneglycol diacetate, and propylene glycol methyl ether acetate; amidesolvents such as N,N-dimethylacetamide, N,N-dimethylformamide, andN-methyl-2-pyrrolidone; ketone solvents such as acetone, methyl ethylketone, methyl isobutyl ketone, acetylacetone, and methyl amyl ketone;and carboxylic ester solvents such as ethyl lactate, methoxymethylpropionate, and ethoxyethyl propionate. These solvents may be used aloneor in combination of two or more thereof.

The amount of the organic solvent to be used in the invention isgenerally from 0.3 to 25 times (by weight) the amount of the siloxanecompound (in terms of the product of complete hydrolysis andcondensation).

The coating composition for use in the invention can be produced bymixing the siloxane compound with an organic solvent together with otheringredients according to need.

OTHER ADDITIVES

The coating composition for use in the invention may further containingredients such as a colloidal silica, colloidal alumina, andsurfactant.

The colloidal silica is a dispersion comprising, for example, any of theaforementioned hydrophilic organic solvents and high-purity silicic acidanhydride dispersed therein. It has an average particle diameter ofgenerally from 5 to 30 nm, preferably from 10 to 20 nm, and a solidconcentration of generally about from 10 to 40% by weight. Examples ofthe colloidal silica include the methanol silica sol and isopropanolsilica sol manufactured by Nissan Chemical Industries, Ltd., and Oscal,manufactured by Catalysts & Chemicals Industries Co., Ltd.

Examples of the colloidal alumina include Alumina Sol 520, 100, and 200,manufactured by Nissan Chemical Industries, Ltd., and Alumina Clear Soland Alumina Sol 10 and 132, manufactured by Kawaken Fine Chemicals Co.,Ltd.

Examples of the surfactant include nonionic surfactants, anionicsurfactants, cationic surfactants, and amphoteric surfactants, andfurther include silicone surfactants, poly(alkylene oxide) surfactants,and poly(meth)acrylate surfactants.

The coating composition for use in the invention preferably has a totalsolid concentration of from 2 to 30% by weight. The total solidconcentration thereof is suitably regulated according to purposes of theuse thereof. When the coating composition has a total solidconcentration of from 2 to 30% by weight, the composition not only givesa coating film having an appropriate thickness but has better storagestability.

In the coating composition for use in the invention, the content ofalcohols having a boiling point of 100° C. or lower is preferably 20% byweight or lower, more preferably 5% by weight or lower. There are caseswhere alcohols having a boiling point of 100° C. or lower generateduring the hydrolysis and condensation of the compounds (1) and (2). Itis therefore preferred to remove such low-boiling alcohols bydistillation or another means so as to result in a content thereof of20% by weight or lower, preferably 5% by weight or lower.

Examples of the substrate to which the coating composition is applied inthe invention include silicon wafers, SiO₂ wafers, and SiN wafers.Usable coating techniques include spin coating, dip coating, rollcoating, and spraying.

The coating film obtained in the invention by applying the coatingcomposition to a substrate and removing the organic solvent therefromhas a thickness of generally from 0.05 to 3 μm, preferably from 0.1 to2.5 μm.

In the invention, the coating film thus formed or an organicsilica-based film obtained by curing the coating film is irradiated withelectron beams.

The irradiation with electron beams according to the invention isconducted at an energy of generally from 0.1 to 50 keV, preferably from1 to 30 keV, in an irradiation dose of generally from 1 to 1,000 μC/cm²,preferably from 10 to 500 μC/cm².

Use of an accelerating voltage of from 0.1 to 50 keV is advantageous inthat electron beams can sufficiently penetrate into inner parts of thecoating film without passing through the film and damaging theunderlying semiconductor device.

Furthermore, when the electron beam irradiation is conducted in anirradiation dose of from 1 to 1,000 μC/cm², the siloxane compound can bereacted throughout the coating film while minimizing damage to thecoating film.

The temperature of the substrate during the electron beam irradiation isgenerally from 25 to 500° C., preferably from 25 to 450° C.

The time required for the coating film to cure with electron beams isgenerally about from 1 to 5 minutes, which is far shorter than the timeof from 15 minutes to 2 hours required for thermal cure. It cantherefore be said that electron beam irradiation is suitable for thetreatment of individual wafers.

Before being irradiated with electron beams according to the invention,the coating film may be converted to an organic silica film having adielectric constant of 3.0 or lower, preferably 2.9 or lower, morepreferably 2.8 or lower, by heating the substrate at from 250 to 500° C.and thereby heat-curing the siloxane ingredient according to theinvention.

The method in which the coating film is heat-cured and then irradiatedwith electron beams is effective in reducing the unevenness of filmthickness attributable to unevenness of electron beam irradiation dose.

The electron beam irradiation in the invention is preferably conductedin an atmosphere having an oxygen concentration of 10,000 ppm or lower,preferably 1,000 ppm or lower.

It is possible to conduct the electron beam irradiation according to theinvention in an inert gas atmosphere. Examples of the inert gas includenitrogen, helium, argon, krypton, and xenon. Preferred of these arehelium, argon and nitrogen. When the electron beam irradiation isconducted in an inert gas atmosphere, the film being irradiated is lessapt to be oxidized, so that a silica-based film retaining a lowdielectric constant can be obtained.

The electron beam irradiation may be conducted in an atmosphere having areduced pressure. The degree of vacuum is generally 133 Pa or lower,preferably from 0.133 to 26.7 Pa.

The silica-based film obtained by the invention has a carbon content(number of carbon atoms) of generally from 5 to 17% by mole, preferablyfrom 9 to 15.5% by mole.

When the silica-based film obtained has a carbon content within thatrange, it can have improved mechanical strength while retaining a lowdielectric constant.

A feature of this silica-based film resides in that it has siliconcarbide bonds (Si—C—Si) within the film structure. In an infraredabsorption spectrum, the silicon carbide bonds give a characteristicabsorption around 890 cm⁻¹.

Because of such features, the silica-based film is excellent ininsulating properties, evenness, dielectric constant characteristics,cracking resistance, and hardness.

Consequently, the silica-based film is useful in applications such asdielectric films for semiconductor devices such as LSIs, system LSIs,DRAMs, SDRAMs, RDRAMs, and D-RDRAMs, protective films such as surfacecoat films for semiconductor devices, dielectric films for multilayeredprinted circuit boards, and protective or insulating films forliquid-crystal display devices.

The invention will be explained below in more detail by reference to thefollowing Examples.

In the following Examples and Production Example, all “parts” and“percents” are by weight unless otherwise indicated.

PRODUCTION EXAMPLE 1

An aqueous solution prepared by dissolving 1.0 g of maleic acid in 157.7g of water was added dropwise over 1 hour at room temperature to asolution prepared by mixing 101.3 g of tetramethoxysilane (40.0 g interms of the product of complete hydrolysis and condensation), 203.0 gof methyltrimethoxysilane (100.0 g in terms of the product of completehydrolysis and condensation), 97.3 g of dimethyldimethoxysilane (60.0 gin terms of the product of complete hydrolysis and condensation), 559.3g of propylene glycol monopropyl ether, and 239.7 g of methyl n-pentylketone. After completion of the addition, the resultant mixture wasreacted at 60° C. for 2 hours and then concentrated under reducedpressure until the total solution amount reached 1,000 g. Thus, aningredient (A) solution having a solid content of 20% was obtained.

PRODUCTION EXAMPLE 2

An aqueous solution prepared by dissolving 1.2 g of maleic acid in 157.7g of water was added dropwise over 1 hour at room temperature to asolution prepared by mixing 152.0 g of tetramethoxysilane (60.0 g interms of the product of complete hydrolysis and condensation), 284.1 gof methyltrimethoxysilane (140.0 g in terms of the product of completehydrolysis and condensation), and 798.8 g of propylene glycol monomethylether. After completion of the addition, the resultant mixture wasreacted at 60° C. for 2 hours and then concentrated under reducedpressure until the total solution amount reached 1,000 g. Thus, aningredient (A) solution having a solid content of 20% was obtained.

PRODUCTION EXAMPLE 3

To a solution prepared by mixing 5 g of 25% aqueous ammonia solution,320 g of ultrapure water, and 600 g of ethanol were added 15 g ofmethyltrimethoxysilane (7.4 g in terms of the product of completehydrolysis and condensation) and 20 g of tetraethoxysilane (5.8 g interms of the product of complete hydrolysis and condensation). Afterthis mixture was reacted at 60° C. for 3 hours, 200 g of propyleneglycol monopropyl ether was added thereto. The resultant mixture wasconcentrated under reduced pressure until the total solution amountreached 140 g. Thereafter, 10 g of a 10% acetic acid solution inpropylene glycol monopropyl ether was added thereto. Thus, a compositionsolution having a solid content of 8.3% was obtained.

PRODUCTION EXAMPLE 4

In 290 g of propylene glycol monopropyl ether were dissolved 77.04 g ofmethyltrimethoxysilane, 24.05 g of tetramethoxysilane, and 0.48 g oftetrakis(acetylacetonato)titanium in a separable flask made of quartz.This solution was stirred with Three-One Motor and the temperature ofthe solution was kept at 60° C. Thereto was added 84 g of ion-exchangedwater over 1 hour. The resultant mixture was reacted at 60° C. for 2hours and 25 g of acetylacetone was then added. This reaction mixturewas further reacted for 30 minutes and then cooled to room temperature.From the reaction mixture was removed 149 g of a solution comprisingmethanol and water by evaporation at 50° C. Thus, a reaction mixture wasobtained.

The product of condensation and other reaction thus obtained had aweight-average molecular weight of 8,900.

PRODUCTION EXAMPLE 5

To a solution prepared by mixing 6 g of 40% aqueous methylaminesolution, 228 g of ultrapure water, and 570 g of ethanol were added 13.6g of methyltrimethoxysilane (6.7 g in terms of the product of completehydrolysis and condensation) and 20.9 g of tetraethoxysilane (6 g interms of the product of complete hydrolysis and condensation). Afterthis mixture was reacted at 60° C. for 2 hours, 200 g of propyleneglycol monopropyl ether was added thereto. The resulting mixture wasconcentrated under reduced pressure until the total solution amountreached 116 g. Thereafter, 10 g of a 10% acetic acid solution inpropylene glycol monopropyl ether was added thereto. Thus, a coatingcomposition 5 having a solid content of 10% was obtained.

EXAMPLE 1

The coating composition 1 obtained in Production Example 1 was appliedto an 8-inch silicon wafer by spin coating to obtain a coating filmhaving a thickness of 0.7 μm. This coating film was heated first at 80°C. in the air for 5 minutes and subsequently at 200° C. in nitrogen for5 minutes and then irradiated with electron beams under the conditionsshown in Table 1.

The film obtained was evaluated by the following methods. The resultsobtained are shown in Table 2.

1. Dielectric Constant

A sample for dielectric constant measurement was produced by forming analuminum electrode pattern by vapor deposition on the film obtained.This sample was examined at a frequency of 100 kHz with precision LCRmeter HP4284A, manufactured by Yokogawa-Hewlett-Packard, Ltd., by the CVmethod to determine the dielectric constant of the coating film.

2. Hardness

A Barkobitch type indenter was attached to a nanohardness meter (tradename: Nanoindentator XP) manufactured by MTS, and this hardness meterwas used to determine the universal hardness of the organic silica-basedfilm formed on the silicon wafer. Hardness was measured by MechanicalProperties Microprobe method.

3. Carbon Content

The number of carbon atoms was determined by the Rutherford backwardscattering method and hydrogen forward coil scattering method. Thecarbon content is shown in terms of the proportion of carbon atoms toall atoms (% by mole).

4. Examination for Silicon Carbide Bond

Whether or not silicon carbide bonds were present was judged by infraredspectroscopy based on the absorption around 890 cm⁻¹ attributable to thestretching vibration of Si—C—Si.

5. Cracking Resistance

The composition sample was applied to an 8-inch silicon wafer by spincoating in such an amount as to result in a cured coating film having athickness of 1.6 μm. This coating film was dried first at 90° C. on ahot plate for 3 minutes and then at 200° C. in a nitrogen atmosphere for3 minutes. Subsequently, the coated substrate was burned for 60 minutesin a 420° C. vacuum oven evacuated to 6.65 Pa. The coating film obtainedwas partly incised with a knife and then immersed in pure water for 5hours. Thereafter, the incision of the coating film was examined with amicroscope to evaluate cracking resistance based on the followingcriteria.

-   -   ∘: No crack propagation was observed.    -   X: Crack propagation was observed.

EXAMPLES 2 TO 7

The coating compositions shown in Table 1 were used in the same manneras in Example 1 to obtain coating films respectively having thethicknesses shown in Table 1. The coating films obtained were heatedfirst at 80° C. in the air for 5 minutes and subsequently at 200° C. innitrogen for 5 minutes and then irradiated with electron beams under theconditions shown in Table 1.

The films obtained were evaluated in the same manner as in Example 1.The results obtained are shown in Table 2.

REFERENCE EXAMPLE 1

The coating composition 1 obtained in Production Example 1 was appliedto an 8-inch silicon wafer by spin coating to obtain a coating filmhaving a thickness of 0.8 μm. This coating film was heated first at 80°C. in the air for 5 minutes and then at 200° C. in nitrogen for 5minutes. Subsequently, the coated wafer was inserted into an electronbeam irradiator and heated therein at 400° C. for 5 minutes withoutconducting electron beam irradiation.

The film obtained was evaluated in the same manner as in Example 1. Theresults obtained are shown in Table 2.

The time required for electron beam irradiation in each of Examples 1 to7 was within 7 minutes.

TABLE 1 Conditions for electron beam irradiation Film AcceleratingIrradiation Ambient Ambient Coating thickness voltage dose temperaturepressure Ambient Example composition (μm) (keV) (μC/cm²) (° C.) (Pa) gasExample 1 1 0.7 5 10 400 1.33 Ar Example 2 3 0.7 7 50 400 1.33 N₂Example 3 2 1.8 15 75 350 1.33 He Example 4 2 1.2 5 100 400 13.3 ArExample 5 1 1.2 3 200 350 1.33 Ar Example 6 3 0.1 1 75 400 93100 ArExample 7 4 0.4 6 50 400 1.33 Ar Reference 1 0.7 No electron beam 4006.65 N₂ Example 1 irradiation

TABLE 2 Carbon Dielectric Hardness content Silicon Constant (GPa) (mol%) carbide Example 1 2.65 0.7 15.3 Present Example 2 2.18 0.7 11.0Present Example 3 2.75 0.9 12.5 Present Example 4 2.78 1.4 12.4 PresentExample 5 2.75 1.1 14.9 Present Example 6 2.22 0.7 11.5 Present Example7 2.55 1.1 15.0 Present Reference 3.11 0.3 10.8 Absent Example 1

EXAMPLES 8 TO 14

Each of the coating compositions shown in Table 3 was applied to an8-inch silicon wafer by spin coating to obtain a coating film having athickness of 0.8 μm. This coating film was heated first at 80° C. in theair for 5 minutes and subsequently at 200° C. in nitrogen for 5 minutesand then cured by heating at 400° C. for 30 minutes to form on thesubstrate an organic silica film having a dielectric constant of 2.8 orlower.

These organic silica films were irradiated with electron beams under theconditions shown in Table 3. The time required for electron beamirradiation in each of Examples 8 to 14 was within 7 minutes.

The films obtained were evaluated in the same manner as in Example 1.The results obtained are shown in Table 4.

TABLE 3 Conditions for electron beam irradiation Film CarbonAccelerating Irradiation Ambient Ambient Coating thickness contentvoltage dose tempeature pressure Ambient Example composition (μm) (mol%) (keV) (μC/cm²) (° C.) (Pa) gas Example 8 4 1.2 13.5 5 10 400 1.33 ArExample 9 5 0.7 10.5 7 50 400 1.33 N₂ Example 2 1.8 12.5 15 75 350 1.33He 10 Example 2 1.2 12.5 5 100 400 13.3 Ar 11 Example 4 1.6 13.5 3 200350 1.33 Ar 12 Example 5 0.1 10.5 1 75 400 93100 Ar 13 Example 4 1.213.5 5 100 250 1.33 Ar 14

TABLE 4 Before electron beam After electron beam irradiation irradiationHardness Si—C—Si Cracking Hardness Si—C—Si Cracking Example k (GPa) bondresistance k (GPa) bond resistance Example 8 2.6 0.71 Absent X 2.6 0.9Present ◯ Example 9 2.3 0.50 Absent ◯ 2.3 0.9 Present ◯ Example 2.2 0.25Absent X 2.2 0.6 Present ◯ 10 Example 2.2 0.25 Absent ◯ 2.2 0.8 Present◯ 11 Example 2.6 0.71 Absent X 2.7 1.1 Present ◯ 12 Example 2.3 0.50Absent ◯ 2.3 0.8 Present ◯ 13 Example 2.6 0.71 Absent X 2.6 1.0 Present◯ 14

According to the invention, a film having a low dielectric constant andexcellent mechanical strength can be provided.

1. A silica-based dielectric film in a semiconductor device obtained bya process comprising applying directly on a semiconductor device a filmcomprising at least one siloxane compound; and irradiating the filmcomprising at least one siloxane compound with electron beams at anirradiation dose of from 1 to 200 μC/cm² to thereby react the siloxanecompound throughout the film and generate silicon carbide bondsrepresented by Si—C—Si while maintaining the dielectric constant of thefilm at a value of 3 or lower, wherein the siloxane compound is aproduct obtained from at least one compound selected from the groupconsisting of compounds represented by the following formula (1):R¹ _(a)Si(OR²)_(4-a)  (1) where R¹ represents a monovalent organic groupor a hydrogen atom; R² represents a monovalent organic group; and a isan integer of 0 to 2, and compounds represented by the following formula(2):R³ _(b)(R⁴O)_(3-b)Si—(R⁷)_(d)—Si(OR⁵)_(3-c)R⁶ _(c)  (2) where R³, R⁴,R⁵, and R⁶ may be the same or different and each represents a monovalentorganic group; b and c may be the same or different and each is aninteger of 0 to 2; R⁷ represents an oxygen atom or a group representedby —(CH₂)_(n)—, where n is 1 to 6; and d is 0 or
 1. 2. The silica-baseddielectric film in a semiconductor device as claimed in claim 1, whereinthe silica-based film has a carbon content of from 5 to 17% by mole. 3.The silica-based dielectric film in a semiconductor device as claimed inclaim 1, wherein the silica-based film is a low-dielectric film.